Worried about debris at canyon mouths

July 28, 2012

As long as Rep. Adam Schiff is asking questions of a federal agency related to the Station fire (“We need answers from Forest Service,” July 15), perhaps he can direct another question toward the U.S. Geological Survey (USGS). Does the USGS consider Los Angeles County's Department of Public Works storing of large amounts of storm debris, much of it from the Station fire, at canyon mouths of low risk to public safety?

The Dunsmore Canyon sediment placement site is a good example of where an extensive residential area is located down slope. Following the Station fire, the USGS examined the increased debris flow risk to the foothill communities of the San Gabriel Mountains. USGS geologists and engineering geologists with an expertise in debris flows will have some opinion on this issue that should be presented to the public.

As a geologist, I believe debris storage at mouths of canyons to be risky business, as these locations are inherently unstable due to erosional processes associated with large debris flows sourced from the mountains, and the possibility the stored debris could make a large debris flow even larger. However, geology is an interpretive science, and it would be worthwhile to hear the opinion of the USGS experts on this question.